1. Field of the Invention
The present invention relates to a technique for calculating toner consumption in an image forming apparatus.
2. Description of the Related Art
In electrophotographic image forming apparatuses, such as printers, copiers and facsimiles, which form images using a toner, a need exists for figuring out toner consumption or residual quantity of toner as a matter of convenience for maintenance services such as toner replenishment. Particularly, the recent years have seen increasing demands for allowing a toner charged in the apparatus to be used as effectively as possible or with minimum toner waste, while exactly predicting time when the toner is used up, as well as for preventing the degradation of image quality as a result of shortage of the remaining toner. Hence, the image forming apparatuses of this type are faced with a demand for further increasing the accuracies of toner counting technique.
In response to such demands, there have heretofore been proposed techniques for accurately determining the toner consumption. According to a calculation method of toner consumption as disclosed in Japanese Patent Application Laid-Open Gazette No. 2002-162800, for instance, the toner consumption is calculated as follows. A cumulative value of a print dot for each color, inputted to a pulse modulator circuit, is integrated on a certain-unit basis, such as on a per-page basis or on a job-unit basis. The resultant integration value is multiplied by a predetermined coefficient. Then, an offset value is added to the product so as to determine the toner consumption for each color.
In the image forming apparatuses of this type, individual apparatuses have delicate distinctions in the characteristics thereof. Even in one apparatus, the characteristics thereof may delicately vary depending upon the use conditions thereof. Because of this, an amount of toner to be used for forming the same image varies from apparatus to apparatus. Under some use conditions, even one apparatus does not always use a constant amount of toner to form each of the same images. However, the prior art has not adequately contemplated this problem. In many cases, therefore, the varied characteristics of the apparatus or the time-related variations of the characteristics of the apparatus make it difficult to determine the toner consumption accurately.
According to the prior-art technique, however, the unit of count is the number of “print dots”, whereas the amount of toner adherent to the intermediate-value dots is calculated on assumption that an equal amount of toner is adhered to each of the dots. That is, the prior-art technique obviates cross study on the amount of toner adherent to the respective types of print dots. As a result, the prior-art technique sometimes falls short of fully meeting the demand for even higher accuracies of the calculation of toner consumption.